More often than not, the positioning of the two shafts is assured, for each of them, by two bearings, namely: a first bearing solely for radial positioning and a second bearing for both radial and axial positioning. However, this answer to the problem does not always afford complete satisfaction, especially when the shafts rotate at high speed, as it necessitates, in fact, two axial stops which give rise to losses of power and necessitate consumption of lubricating oil. Moreover, the coupling device itself sometimes gives rise to parasitic axial forces of such a character as cause exceptional wear and tear to the stops.
Another current arrangement consists in providing axial stops on one only of the two shafts, while the coupling device is formed and arranged both to transmit the torque and to assure the axial connection between the two shafts. This arrangement thus enables the number of thrust bearings to be reduced and, moreover, it assures more or less a balancing of the axial forces between the two shafts, while greatly reducing the consumptions of power and of oil. There are numerous coupling devices of this kind in which the transmission of the torque is effected generally by sets of teeth, while the axial connection is assured by arrangements with or without play and, should the occasion arise, comprising resilient arrangements. However, they are relatively complicated and cumbersome.